sign_demo.cc

int sign(uint8_t *msg, size_t msglen, std::string sha_alg)
{
    if (!evp_sign_key || !privatekey) {
        std::cerr << "invalid sign key or private key is not loaded" << std::endl;
        return -1;
    }

    const EVP_MD *md;

    // mark the sha alg to use
    if (sha_alg == "sha256") {
        md = EVP_sha256();
    } else if (sha_alg == "sha1") {
        md = EVP_sha1();
    } else {
        return -1;
    }

    int ret;

    EVP_MD_CTX *mdctx = EVP_MD_CTX_create();

    ret = EVP_DigestSignInit(mdctx, NULL, md, NULL, evp_sign_key);
    if (ret != 1) {
        ERR_print_errors_fp(stderr);
        return -1;
    }

    ret = EVP_DigestSignUpdate(mdctx, msg, msglen);
    if (ret != 1) {
        ERR_print_errors_fp(stderr);
        return -1;
    }

    ret = EVP_DigestSignFinal(mdctx, signature, &signature_len);
    if (ret != 1) {
        ERR_print_errors_fp(stderr);
        return -1;
    }

    EVP_MD_CTX_destroy(mdctx);

    std::cout << "signature generated : " << signature_len << " bytes" << std::endl;

    return 0;
}